Dish reflector for a high gain antenna

ABSTRACT

A dish reflector for a high antenna formed by a plurality of generally triangular petals joined edgewise to form a quasiparaboloid configuration.

United States Patent Taggart, Jr. I

[451 Aug. 27, 1974 DISH REFLECTOR FOR A HIGH GAIN ANTENNA [76] lnventor:Robert B. Taggart, Jr., 575 So.

Rengstarff Ave., Apt. 95, Mountain View, Calif. 94040 [22] Filed: Mar.3, 1972 ['21] Appl. No.: 231,673

[52] US. Cl. 343/840, 343/915 [51] Int. Cl. ,H0lq 15/20 [58] Field ofSearch 343/840, 912, 915

[56] References Cited UNITED STATES PATENTS 2/1966 Thomas 343/9123,235,872 2/1966 Schepis 343/912 3,397,399 8/1968 Charman et a1. 343/9153,438,045 4/1969 Braccini 343/912 Primary ExaminerEli LiebermanAttorney, Agent, or FirmPaul B. Fihe [57] ABSTRACT A dish reflector fora high antenna formed by a plurality of generally triangular petalsjoined edgewise to form a quasi-paraboloid configuration.

6 Claims, 6 Drawing Figures DISH REFLECTOR FOR A HIGH GAIN ANTENNA FIELDOF THE INVENTION The present invention relates generally to antennas,and more particularly, to a dish reflector for a high-gain antenna.

The invention described herein was made in the performance of work undera NASA contract and is subject to the provisions of Section 305 of theNational Aeronautics and Space Act of 1958, Public Law 85-568 (72 Stat.435/ 42 U.S.C. 2457).

BACKGROUND OF THE INVENTION A high-gain antenna is an obvious necessityto provide an intelligible signal when the received electromagneticenergy is at a relatively low power level. For example, an ordinarytelevision antenna having relatively low-gain characteristics isperfectly satisfactory to produce intelligible sound and a cleartelevision picture when located within line of sight of a conventionaltelevision transmitting station. On the other hand, a television orother communication signal transmitted from a satellite in orbitobviously arrives at an intercepting antenna with a relatively low powerlevel of electromagnetic energy wherefore the use of a highgain antennais imperative. Commonly, such a highgain antenna takes the form of arelatively large size paraboloid reflector which receives the radiatedelectromagnetic energy over its entire surface and in accordance withthe general reflective characteristic of a paraboloid, reflects suchenergy to a collector located at its focal point.

Recently, proposals for the wide dissemination of educationalinformation to remote areas have included the provision of a pluralityof television receivers arranged in such remote areas to receive thetelevision signal emanating from a satellite. The number and remotelocations of these plural receiving stations present practical problemsin the shipping, local installation and cost. More particularly, boththe size and shape of a true paraboloid do not lend themselves readilyto mass production techniques; thus the cost is high. If a unitarystructure, shipping and handling are a problem; if composed of aplurality of compound curvature sections, yet added cost and assemblycomplexity appear.

SUMMARY OF THE PRESENT INVENTION Accordingly, it is the generalobjective of the present invention to provide a high-gain antenna whichincorporates a dish reflector formed from a number of parts capable offabrication by mass production techniques wherefore the costs areminimized and the elements can readily be shipped in their disassembledform in a relatively compact light weight package but subsequentlyassembled and installed in operating condition quickly, easily, and withassurance of high-gain performance.

Generally, the dish reflector is formed by the assembly of a pluralityof generally triangular reflector petals in substantially edgewise,abutting relationship to form a dish in the form of a quasi-paraboloid.Generally the term, quasi-paraboloid, refers to a dish reflectorstructure wherein a section line extending outwardly from the center ofthe antenna through'the center of one of the petals has an approximateparabolic configuration whereas a section line transverse to suchoutwardly extending line remains substantially rectilinear. Moreparticularly, the generally paraboloid curvature of each individualpetal outwardly from the center of the reflector dish is determined bythe precise positions of connection of adjoining petals and is designedto minimize the phase errors resultant from the departure of thereflector conformation from that of a true paraboloid.

In order to simplify and reduce manufacturing costs of the dishreflector, each of the petals is initially formed, in one case, by asimple blanking operation, in a flat, generally triangular form fromsheet aluminum, steel, or other material having a highly reflectivesurface and in particular being capable of bending during assembly toform the ultimate quasi-paraboloid shape. During the blanking operation,holes are formed along the edges of the petals in predeterminedcalculated disposition so'that upon subsequent assembly of the petals inedgewise abutting relation through the use of nuts and bolts, poprivets, or other connecting means, the desired quasi-paraboloidconformation will automatically be achieved thus eliminating the needfor any skill or technical know-how on the part of the person assemblingthe structure.

Preferably, rim segments are arranged to receive the outer edges of thetriangular petals during installation and adjacent rim segments are inturn joined by the simple bolted connection of angular corner bracketsthereto so as to function as assembly jigs during the assembly operationand to subsequently function as a rigid exterior rim structure for thedish reflector enabling it to withstand mechanical shock and alsoenabling appropriate mounting of the dish reflector in the desireddisposition for optimum reception of the electromagnetic radiation.

Obviously, the disassembled petals, rim segments, and corner bracketscan be shipped in a rather compact package even though the ultimate sizeof the assembled dish reflector is relatively large, yet upon arrival,use of but simple tools by a relatively unskilled person enableserection of the dish reflector in a period of less than two hours.Because of the pre-established petal dimensions and the holes thereinwhich control the configuration of the assembled reflector, the desiredhigh-gain is assured.

The quasi-paraboloid configuration can obviously be obtained in otherspecific fashions, one example being the edgewise connection of aplurality of generally triangular reflective petals to preformed, rigidribs projecting radially in a generally parabolic configuration,enabling the elimination of the exterior rim segments.

BRIEF DESCRIPTION OF THE DRAWINGS The stated objective of the inventionand the manner in which it is achieved as summarized hereinabove willbecome more readily apparent from a perusal of the following detaileddescription of exemplary embodiments of the invention illustrated in theaccompanying drawings wherein:

FIG. 1 is a perspective view of a microwave antenna incorporating a dishreflector in accordance with the present invention,

FIG. 2 is an enlarged, fragmentary, sectional view taken along line 2-2of FIG. 1 illustrating certain structural details of the dish reflector,

FIG. 3 is another enlarged, fragmentary, sectional view taken along line3-3 of FIG. 1 illustrating yet further structural details,

FIG. 4 is an exploded view of the parts indicating the manner ofassembly of the dish reflector of FIG. 1,

FIG. 5 is a three-axis diagram explanatory of the manner in which gainof the reflector is maximized, and

FIG. 6 is an exploded, perspective view similar to FIG. 4 of the partsof a modified dish reflector embodying the invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS OF THE INVENTION Withinitial reference to FIG. '1, a high-gain antenna is illustrated andincludes in accordance with the present invention, a dish reflector 10whose interior surface is formed from highly reflective material, andspecifically has the conformation of a quasi-paraboloid whichconformation will be more precisely defined hereinafter. Threesupporting legs 12 project upwardly from a rigid base 14 to engage andsupport the rim of the dish reflector 10 in proper orientation so thatthe Z axis of the quasi-paraboloid, as indicated in FIG. 1, is directedtowards a satellite or other source of radiation which is to bereflected by the reflector towards a suitable collector 16 supported bysuitable arms 18 projecting upwardly and inwardly from spaced points onthe rim of the reflector so that such collector will reside also on theZ axis and more particularly at the focal point of the quasi-paraboloidso that, as will be explained in greater detail hereinafter, and as inthe case of true paraboloid reflectors, the reflected electromagneticenergy will be focused at such collector 16 whose output in turn afterappropriate electronic processing is fed through a feed line indicatedat 20 to a conventional television set .(not shown). It will be obviousthat the collected energy can alternatively provide an input signal to asound receiver or other form of electronic equipment and such receivingequipment forms no part of the present invention, in and of itself.Furthermore, as will be apparent, a simple electronic reversal enablesdelivery of energy to the antenna dish for transmission rather thanreception of electromagnetic energy.

As specifically illustrated in FIG. 1, the dish reflector 10 is formedby ten petals 22 of highly reflective material, each petal subtending anangle of 36 at its central apex and curving outwardly so that in centralsection through its altitude defines substantially a parabola, as shownin FIG. 2. A section line at right angles or transverse to the altitudeof each triangular petal 22 on the other hand is rectilinear as shown inFIG. 3 so that slight deviations from a true paraboloid result. Thedescribed and illustrated conformation of all of the reflector petals 22is the same and the totality of the conformation of the 10 petals isencompassed by the mentioned term, quasi-paraboloid.

Preferably, the individual petals 22 are formed from rather thin andflexible aluminum sheet (e'.g., 0.040 inch) and to add structuralrigidity to the arrangement, the outer edge or base of each triangularpetal is supported in a slot 24 at one side of a boxlike rim segment 26which is preferably formed as an extruded aluminum section (see FIG. 4)and the closely abutting ends of adjoining rim segments 26 are in turnjoined rigidly by angular comer brackets 28 which encompass the adjacentrim segments and are joined to the rim segments and the outer corners ofthe petals 22 by suitable nuts and bolts indicated at 30. In turn, theadjoining edges of the petals 22 have a plurality of holes 32 at spacedintervals therealong and are arranged in overlapping relation as shownin FIG. 3 so that they can be joined by the application of pop rivets34, as shown, or alternatively by any other form of connecting meanssuch as a simple nut and bolt arrangement.

Preferably, as illustrated in FIG. 4, each of the individual, generallytriangular petals 22 is initially formed by blanking in essentially aflat configuration, but since it is formed from slightly flexiblematerial such as the thin aluminum mentioned hereinabove, each petal iscapable of being bent in single curvature so that the altitude of theassembled triangular'petal will approximate the parabolic configurationdescribed hereinabove and shown in FIG. 2, while retaining a rectilineardisposition in the transverse direction as shown and described inconnection with FIG. 3. The desired configuration is obtained inaccordance with the present invention by precisely positioning the holesalong the adjacent edges of the petal sections so that when the poprivets 34 are applied thereto, the individual petals 22 are bent to thedesired singly curved conformation.

The assembly operation is extremely simple once the petals 22 have beenso formed with the required exterior dimensions and the desired holedispositions. Initially, two of the rim segments 26 are assembled withthe angular comer bracket 28 and two adjacent petals 22 are then slippedinto the adjoining rim segments so as to lie in edgewise overlappingrelationship. The bolts 30 are manually applied to the bracket segmentsand other corners of the petals. The first pop rivet 34 is then appliedto the outermost, overlapping holes 32 of the two petals, the desiredregistration of the holes being readily attained by a slight bending ofthe adjacent petals. Thereafter, additional pop rivets 34 or otherconnecting means are applied in succession to the registering holes 32in the adjacent petals 22 and upon completion of the riveting operation,the desired quasiparaboloid configuration is attained. It is to beparticularly noted that the bracket 28 and rim segments 26 function,during such assembly operation, as assembly jigs to facilitate ease andrapidity in the assembly of the dish reflector.

When the assembly is completed, even though the petals 22 themselves arerelatively thin material, the rim segments 26 and brackets 28 joinedthereto form a mechanically rigid structure so that the assembled dishreflector 10 will retain its shape regardless of weather conditions ormechanical shock.

In view of the fact that the assembled dish reflector 10 is aquasi-paraboloid, the path lengths of radiation from a plane wave frontreflected at different points to the focus will have regular variationsin comparison to the corresponding path lengths utilizing a trueparaboloid. Such differences in path lengths will in turn result inslight phase errors of the reflected electromagnetic energy, but bysuitable design criteria to be described in detail hereinafter, thesephase errors are minimized so that the realizable gain of the ten petalantenna as specifically described hereinabove is reduced by no more thana fraction of a decibel below that achievable by a perfect paraboloid.

More particularly, and with reference to the diagrammatic showing of.FIG. 5, the distance traveled bu an electromagnetic wave from an XYplane 36 through the focal point 38 of the quasi-paraboloid willinitially travel a distance [F Z (y)] to a point 40 on the reflectivepetal 22 and will thereafter travel from this point 40 to the focalpoint 38 a distance, L =([F -Z (y)] x y fi, the total distance, d, beingequal to the sum, [F Z(y)] ([F Z(y)] x y It being known that thedistance from a plane through the focus to a perfect paraboloid andthence to the focal point is equal to 2F (F being the focal distance asindicated) in accordance with the general definition of a paraboloid,the difference in distance which we will refer to as the phase errordistance will be (2F d). In order to minimize the phase error asdesired, it is merely necessary then to determine the amount of bendingof the petal 22 to provide a dimension Z y) such that the quantity,

r 1 01) d I I (2F-d) y=0 1:0 U)

is a minimum, r being the radius of the antenna, and w( y) thehalf-width of a single petal.

Knowing the value Z,,,,,,(y), it is then but a simple geometrictransformation to find the precise shape of a petal 22 and the holedispositions to produce the requisite amount of bending to provideZ,,,,,,(y) and the consequent minimized phase error. By way of example,in one particular dish reflector designed for operation at 2.62 GHz witha reflector diameter of approximately 7 feet, the individual petals 22as stamped in their flat triangular form had an altitude of 43.5 inchesand the precise X and Y dimensions of the individual petal holes, asindicated in FIG. 4, were as follows measured from the center or apex ofthe triangular petal outwardly:

0.487 0.500 1.462 3.504 2.437 6.5l6 3.4 l 2 9.546 4.386 l2.598 5.361l5.677 6.255 l8.53l 7.229 2 l .680 8.l23 24.606 9.0l7 27.575 9.9l030.589

10.804 33.655 l L697 36.768 l2.509 39.656 13.322 42.587

The mechanical tolerances in the hole dispositions was maintained at0.005 inch which is well within the capability of standard massproduction blanking techniques and with this particular reflectorconfiguration, an antenna gain of 32 dB was attained which is but 0.9 dB

below that of a perfect paraboloid. It will be apparent be achieved byan unskilled laborer in less than 2 hours, and the resultant reflectordish has excellent gain.

The number of petals can accordingly be changed without departing fromthe spirit of the invention and other changes such as integrating therim segments with the petals will similarly suggest themselves.Additionally, the petals and supports therefor can be considerablymodified while retaining the quasi-paraboloid conformation. By way ofexample, in FIG. 6, petals 42 formed of expanded metal which is flexibleand highly reflective are joined at their edges by machine screws 44 toradially extending parabolic ribs 46 formed from rigid metal straps withsuitable threaded holes therein. A radial section through each petal 42is substantially parabolic but a transverse section is substantiallyrectilinear as in the first embodiment so that the simple structural butexcellent gain characteristics are again achieved.

Additional modifications and/or alterations can obviously be madewithout departing from the spirit of the invention. Accordingly, theforegoing description of but two embodiments of the invention is to beconsidered as purely exemplary and not in a limiting sense, and theactual scope of the invention is to be indicated only be reference tothe appended claims.

What is claimed is:

1. A dish reflector for a high-gain antenna which comprises a pluralityof generally triangular reflective petals and means connecting saidpetals in edgewise overlapping relation to form a quasi-paraboloid witha line extending centrally outward through each petal being of generallyparabolic form and a transverse line being substantially rectilinear,

said connecting means including a plurality of connecting membersjoining the overlapping edges of said petals through registered holestherein at predetermined dispositions which define the ultimateassembled quasi-paraboloid conformation of the reflector.

2. A dish reflector according to claim 1 wherein the generally paraboliccurvature of each petal outwardly is such that the phase errors ofreflected electromagnetic energy at the focus of the quasiparaboloid areminimized.

3. A dish reflector according to claim 1 which comprises a rigid rimconnected to the exterior edges of said petals to provide structuralrigidity.

4. A dish reflector according to claim 3 wherein said rim includes aplurality of rim segments slotted to receive the outer edges of saidpetals and joined at the extremities by angular corner brackets.

5. A dish reflector according to claim 1 wherein said petals, prior toconnection by said connecting means, are in the form of flat sheets offlexible material.

6. A dish reflector according to claim 1 wherein said petals are formedof flexible material.

1. A dish reflector for a high-gain antenna which comprises a pluralityof generally triangular reflective petals and means connecting saidpetals in edgewise overlapping relation to form a quasi-paraboloid witha line extending centrally outward through each petal being of generallyparabolic form and a transverse line being substantially rectilinear,said connecting means including a plurality of connecting membersjoining the overlapping edges of said petals through registered holestherein at predetermined dispositions which define the ultimateassembled quasi-paraboloid conformation of the reflector.
 2. A dishreflector according to claim 1 wherein the generally parabolic curvatureof each petal outwardly is such that the phase errors of reflectedelectromagnetic energy at the focus of the quasi-paraboloid areminimized.
 3. A dish reflector according to claim 1 which comprises arigid rim connected to the exterior edges of said petals to providestructural rigidity.
 4. A dish reflector according to claim 3 whereinsaid rim includes a plurality of rim segments slotted to receive theouter edges of said petals and joined at the extremities by angularcorner brackets.
 5. A dish reflector according to claim 1 wherein saidpetals, prior to connection by said connecting means, are in the form offlat sheets of flexible material.
 6. A dish reflEctor according to claim1 wherein said petals are formed of flexible material.